Automotive lamp

ABSTRACT

A lighting circuit turns on multiple semiconductor light sources. Multiple current sources are each coupled in series with a corresponding one from among the semiconductor light sources. A switching converter supplies a driving voltage VOUT across each of multiple series connection circuits formed of the multiple semiconductor light sources and the multiple current sources. A converter controller controls a switching transistor of the switching converter based on a relation between a voltage across one from among the multiple current sources and a reference voltage having a positive correlation with the temperature Tj.

BACKGROUND 1. Technical Field

The present disclosure relates to a lighting circuit.

2. Description of the Related Art

Typical automotive lamps are capable of switching between a low-beammode and a high-beam mode. The low-beam mode is used to illuminate aclose range in the vicinity of the user's vehicle with a predeterminedlight intensity. In the low-beam mode, light distribution is determinedso as to prevent glare being imparted to an oncoming vehicle or aleading vehicle. The low-beam mode is mainly used when the vehicle istraveling in an urban area. In contrast, the high-beam mode is used toilluminate a distant range over a wide area ahead of the vehicle with arelatively high light intensity. The high-beam mode is mainly used whenthe vehicle is traveling at high speed along a road where there are asmall number of oncoming vehicles and leading vehicles. Accordingly, thehigh-beam mode provides the driver with high visibility, which is anadvantage, as compared with the low-beam mode. However, the high-beammode has a problem of imparting glare to a pedestrian or a driver of avehicle ahead of the vehicle.

In recent years, the Adaptive Driving Beam (ADB) technique has beenproposed in which a high-beam distribution pattern is dynamically andadaptively controlled based on the state of the surroundings of avehicle. With the ADB technique, the presence or absence of a leadingvehicle, an oncoming vehicle, or a pedestrian ahead of the vehicle isdetected, and the illumination is reduced or turned off for a regionthat corresponds to such a vehicle or pedestrian thus detected, therebyreducing glare imparted to such a vehicle or pedestrian.

FIG. 1 is a block diagram showing a lamp system 1001 having an ADBfunction. The lamp system 1001 includes a battery 1002, a switch 1004, aswitching converter 1006, multiple light-emitting units 1008_1 through1008_N, multiple current sources 1010_1 through 1010_N, a convertercontroller 1012, and a light distribution controller 1014.

The multiple light-emitting units 1008_1 through 1008_N are eachconfigured as a semiconductor light source such as a light-emittingdiode (LED), laser diode (LD), or the like, which are associated withmultiple different regions on a virtual vertical screen ahead of thevehicle. The multiple current sources 1010_1 through 1010_N are arrangedin series with the multiple corresponding light-emitting units 1008_1through 1008_N. A driving current I_(LEDi) generated by the currentsource 1010_i flows through the i-th (1≤i≤N) light-emitting unit 1008_i.

The multiple current sources 1010_1 through 1010_N are each configuredto be capable of turning on and off (or adjusting the amount of current)independently. The light distribution controller 1014 controls theon/off state (or the amount of current) for each of the multiple currentsources 1010_1 through 1010_N so as to provide a desired lightdistribution pattern.

The switching converter 1006 configured to provide a constant voltageoutput generates a driving voltage V_(OUT) that is sufficient for themultiple light-emitting units 1008_1 through 1008_N to provide lightemission with a desired luminance. Description will be made directingattention to the i-th channel. When a given driving current I_(LEDi)flows through the light-emitting unit 1008_i, a voltage drop (forwardvoltage) V_(Fi) occurs in the light-emitting unit 1008_i. In order toallow the current source 1010_i to generate the driving currenti_(LEDi), the voltage across the current source 1010_i is required to belarger than a particular voltage (which will be referred to as“saturation voltage V_(SATi)” hereafter). Accordingly, the followinginequality expression must hold true for the i-th channel.V _(OUT) >V _(Fi) +V _(SATi)  (1)

This relation must hold true for all the channels.

Problem 1

In order to satisfy the inequality expression (1) in all situations, theoutput voltage V_(OUT) may preferably be employed as the control targetfor the feedback control. Specifically, as represented by Expression(2), a target value V_(OUT(REF)) of the output voltage V_(OUT) is set toa higher value giving consideration to a margin. Furthermore, the outputvoltage V_(OUT) may preferably be feedback controlled such that theoutput voltage V_(OUT) of the switching converter 1006 matches thetarget value V_(OUT(REF)).V _(OUT(REF)) =V _(F(MARGIN)) +V _(SAT(MARGIN))  (2)

Here, V_(F(TYP)) represents the maximum value (or typical value) ofV_(F) with a margin added. V_(SAT(MARGIN)) represents a saturationvoltage V_(SAT) with a margin added.

In this control operation, the difference between the saturation voltageV_(SAT(MARGIN)) and the actual saturation voltage V_(SAT) is applied tothe current source 1010, which leads to the occurrence of unnecessarypower loss. In addition, when the actual forward voltage V_(F) is lowerthan V_(F(MARGIN)), voltage drop that occurs across the current source1010 includes the voltage difference between them, leading to theoccurrence of unnecessary power loss.

With an automotive lamp, there is a need to flow a very large currentthrough a light-emitting unit. Furthermore, it is more difficult toprovide such an automotive lamp with countermeasures for releasing heatthan it is for other devices. Accordingly, with the automotive lamp,there is a demand to reduce the heat amount due to the current source asmuch as possible.

Problem 2

The spatial resolution of the light distribution pattern generated bythe lamp system 1001 is determined by the number N of the light-emittingunits 1008. With a lamp system that supports high spatial resolution inwhich the number N exceeds several hundred, such a system has a problemof an increased number of lines that couple elements or circuits. As anexample, in a case in which such light-emitting units are arranged inthe form of a matrix with 30 pixels in the vertical direction and 30pixels in the horizontal direction, the light distribution controller1014 and the multiple light-emitting units 1008 are coupled via N (=900)signal lines, which is unrealistic.

FIG. 22 is a diagram showing another example configuration of the lampsystem 1001. The multiple current sources 1010_1 through 1010_N areintegrated on a single semiconductor chip (driving IC) 1020. Aninterface/decoder circuit 1022 is mounted on the driving IC 1020.Furthermore, control signals for the N current sources 1010_1 through1010_N are transmitted in a time-sharing manner. This allows the numberof lines that couple the driving IC 1020 and the light distributioncontroller 1014 to be reduced. In a case in which high-speed serialcommunication is employed, such an arrangement requires only severallines.

By investigating the lamp system 1001 shown in FIG. 22 , the presentinventor has recognized the following problem.

With the lamp system shown in FIG. 1 , when an abnormal state hasoccurred in a line between a current source 1010 and the lightdistribution controller 1014, this leads to the occurrence of anout-of-control state in the light-emitting unit 1008 that corresponds tothe line. However, there is a low probability of the occurrence of anabnormal state in all N lines. Accordingly, in actuality, this does notimmediately lead to a state in which the vehicle cannot be driven.

In contrast, with the lamp system shown in FIG. 22 , all thelight-emitting units 1008 are controlled via several lines 1030.Accordingly, even when only a single line 1030 comes to be in anabnormal state, this leads to the occurrence of an out-of-control statein all the light-emitting elements 1008. This leads to a situation inwhich an oncoming vehicle or a leading vehicle is disturbed, or asituation in which a necessary area cannot be illuminated.

The same problem can occur in other kinds of lamps. FIG. 23 is anotherexample configuration of an automotive lamp. An automotive lamp 2001includes a lamp ECU 2002, an interface 2010, a local controller 2020, avariable light distribution device 2030, a light source 2040, and alighting circuit 2050.

The lighting circuit 2050 turns on the light source 2040. The variablelight distribution device 2030 includes multiple independentlycontrollable elements. A light distribution pattern is generatedaccording to the state of the multiple controllable elements. Forexample, the variable light distribution device 2030 is configured as aDigital Mirror Device (DMD) configured to reflect the output light ofthe light source 2040. The variable light distribution device 2030 isconfigured such that a reflection on/off state is controllable for eachpixel.

Alternatively, in a case in which the automotive lamp 2001 employs abypass method, the light source 2040 includes multiple LEDs coupled inseries. The variable light distribution device 2030 includes multiplebypass switches respectively coupled in parallel with the multiple LEDs.The light distribution pattern is generated according to the on/offstates of the multiple bypass switches.

In a case in which the variable light distribution device 2030 and thelocal controller 2020 are mounted on a circuit board 2006 that isseparate from that on which the lamp ECU 2002 is mounted, the lamp ECU2002 and the local controller 2020 are coupled via a communication line2004 instead of wiring provided on a printed circuit board. The circuitboard 2006 includes the interface circuit 2010 that receives a controlsignal S1 from the lamp ECU 2002.

The local controller 2020 converts the control signal S1 received by theinterface circuit 2010 into individual control signals S2 for indicatingthe states of the multiple controllable elements included in thevariable light distribution device 2030.

In this case, when an abnormal state has occurred in the communicationline 2004, the connector, the lamp ECU 2002, or the communication line 5that couples the lamp ECU 2002 and the in-vehicle ECU 4 configured as anupstream stage, this leads to the occurrence of an out-of-control statein the variable light distribution device 2030. This means that anoncoming vehicle or a leading vehicle is disturbed or that a necessaryarea cannot be illuminated.

SUMMARY

1. A lighting circuit according to one embodiment of the presentdisclosure relates to a lighting circuit structured to turn on and offmultiple semiconductor light sources. The lighting circuit includes:multiple current sources each of which is to be coupled in series with acorresponding one from among the multiple semiconductor light sources; aswitching converter structured to supply a driving voltage across eachof multiple series connection circuits each of which includes one of themultiple semiconductor light sources and one of the multiple currentsources; and a converter controller structured to control the switchingconverter based on a relation between the voltage across one of themultiple current sources and a reference voltage having a positivecorrelation with temperature.

2. Another embodiment of the present disclosure relates to a drivercircuit structured to supply a driving current to multiple semiconductorlight sources. The driver circuit includes: multiple current sourceseach of which is to be coupled in series with a corresponding one fromamong the multiple semiconductor light sources; an interface circuitcoupled to a processor, and structured to receive a control signal forindicating the on/off state of each of the multiple semiconductor lightsources, to generate multiple individual control signals based on thecontrol signal so as to set the on/off state of each of the multiplecurrent sources; and a protection circuit structured to monitorcommunication between the processor and the interface circuit, and toforcibly set each of the multiple current sources to a predeterminedstate when an abnormal state has been detected.

Yet another embodiment of the present disclosure relates to anautomotive lamp. The automotive lamp includes: a higher-levelcontroller; an interface circuit structured to receive a control signalfrom the controller; a variable light distribution device; a localcontroller structured to control the variable light distribution devicebased on the control signal received by the interface circuit; and aprotection circuit structured to monitor communication between theprocessor and the interface circuit, and to forcibly set a predeterminedpattern for the variable light distribution device when an abnormalstate has been detected.

It should be noted that any combination of the components describedabove, any component of the present disclosure, or any manifestationthereof, may be mutually substituted between a method, apparatus,system, and so forth, which are also effective as one embodiment of thepresent disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, withreference to the accompanying drawings which are meant to be exemplary,not limiting, and wherein like elements are numbered alike in severalFigures, in which:

FIG. 1 is a block diagram showing a lamp system having an ADB function;

FIG. 2 is a block diagram showing a lamp system including an automotivelamp according to an embodiment 1;

FIG. 3 is an operation waveform diagram showing the operation of theautomotive lamp shown in FIG. 2 ;

FIG. 4A is a waveform diagram showing the cathode voltage V_(LED) in theembodiment 1, and FIG. 4B is a waveform diagram showing the cathodevoltage V_(LED) in a comparison technique;

FIG. 5 is a circuit diagram showing an example configuration of multiplecurrent sources;

FIG. 6A is a diagram showing the I-V characteristics of a MOStransistor, and FIG. 6B is a diagram showing a relation between thetemperature and the overdrive voltage.

FIG. 7 is a circuit diagram showing a converter controller according toan example 1-1;

FIG. 8 is a circuit diagram showing an example of a voltage generatingcircuit that generates the bottom limit voltage V_(BOTTOM);

FIG. 9 is another example of the voltage generating circuit thatgenerates the bottom limit voltage V_(BOTTOM);

FIG. 10 is a circuit diagram showing a converter controller according toan example 1-2;

FIG. 11 is a circuit diagram showing a converter controller according toan example 1-3;

FIG. 12 is a circuit diagram showing a converter controller according toan example 1-4;

FIG. 13 is a circuit diagram showing a converter controller according toan example 1-5;

FIG. 14 is a circuit diagram showing a converter controller according toan example 1-6;

FIG. 15 is a circuit diagram showing a specific configuration of theconverter controller shown in FIG. 14 ;

FIG. 16 is a circuit diagram showing a modification of an on signalgenerating circuit;

FIG. 17A through 17C are circuit diagrams each showing an exampleconfiguration of the current source;

FIG. 18 is a circuit diagram showing a current driver IC and aperipheral circuit thereof according to an embodiment 2;

FIG. 19 is an operation waveform diagram showing the operation of thecurrent driver IC;

FIG. 20 shows a plan view and a cross-sectional view of anintegrated-driver light source.

FIG. 21 is a circuit diagram showing an automotive lamp according to amodification 1-3;

FIG. 22 is a diagram showing another example configuration of the lampsystem;

FIG. 23 is a diagram showing another example configuration of theautomotive lamp;

FIG. 24 is a block diagram showing a lamp system including theautomotive lamp according to an embodiment 3;

FIG. 25 is a circuit diagram showing an example configuration ofmultiple current sources;

FIG. 26 is a plan view of an LED chip;

FIG. 27 is a block diagram showing an example configuration of aninterface circuit and a protection circuit;

FIGS. 28A and 28B are circuit diagrams each showing an exampleconfiguration of a data replacement circuit;

FIG. 29 shows a plan view and a cross-sectional view of theintegrated-driver light source;

FIG. 30 is a circuit diagram showing the automotive lamp according to amodification 3.1;

FIG. 31 is a block diagram showing an automotive lamp according to anembodiment 4;

FIG. 32 is a block diagram showing the automotive lamp according to amodification 4.1; and

FIG. 33 is a block diagram showing the automotive lamp according to amodification 4.2.

DETAILED DESCRIPTION Overview of the Embodiments

A summary of several example embodiments of the disclosure follows. Thissummary is provided for the convenience of the reader to provide a basicunderstanding of such embodiments and does not wholly define the breadthof the disclosure. This summary is not an extensive overview of allcontemplated embodiments, and is intended to neither identify key orcritical elements of all embodiments nor to delineate the scope of anyor all aspects. Its sole purpose is to present some concepts of one ormore embodiments in a simplified form as a prelude to the more detaileddescription that is presented later. For convenience, the term “oneembodiment” may be used herein to refer to a single embodiment ormultiple embodiments of the disclosure.

1. One embodiment disclosed in the present specification relates to alighting circuit structured to turn on and off multiple semiconductorlight sources. The lighting circuit includes: multiple current sourceseach of which is to be coupled in series with a corresponding one fromamong the multiple semiconductor light sources; a switching converterstructured to supply a driving voltage across each of multiple seriesconnection circuits configured of the multiple semiconductor lightsources and the multiple current sources; and a converter controllerstructured to control the switching converter based on a relationbetween the voltage across one from among the multiple current sourcesand a reference voltage having a positive correlation with temperature.

In a case in which the reference voltage is designed to be a minimumlevel that ensures that the current sources are each able to generate apredetermined amount of driving current in a sure manner, therebyallowing power loss in the current sources to be reduced. In a case inwhich the reference voltage is maintained at a constant value that isindependent of the temperature, (i) when the reference voltage is set toa high voltage, such an arrangement is able to maintain the drivingcurrent at a predetermined amount even in a high-temperature state.However, such an arrangement has a problem of increased power loss whenthe temperature becomes low. Conversely, (ii) when the reference voltageis set to a low voltage, such an arrangement allows the power loss to bereduced in a low-temperature state. However, when the temperaturebecomes high, such an arrangement is not able to maintain the drivingcurrent at a predetermined amount, leading a reduction in the luminanceof the semiconductor light sources. In contrast, in a case in which thereference voltage is changed based on a positive correlation with thetemperature, this arrangement provides both an advantage of low powerconsumption in a low-temperature state and an advantage of maintainingthe driving current in a high-temperature state.

Also, the converter controller may turn on a switching transistor of theswitching converter in response to a reduction to the reference voltagein the voltage across one from among the multiple current sources.

Also, the current source may include a current mirror circuit. In thiscase, in a case in which the reference voltage is adjusted based on thetemperature dependence of the pinch-off voltage (overdrive voltage) ofthe MOS transistors or the collector saturation voltage V_(CE(sat)) ofbipolar transistors that form the current mirror circuit, thisarrangement allows the power consumption to be reduced.

Also, the converter controller may include: a constant voltage sourcestructured to generate a constant voltage; and a correction currentsource structured to generate a correction current having a positivecorrelation with temperature. Also, the reference voltage may match thevoltage obtained by adding the constant voltage to an offset voltagethat is proportional to the correction current.

Also, the correction current may be generated using a temperaturedependence of a forward voltage provided by a PN junction.

Also, the correction current source may include: at least one diode anda resistor coupled in series; and a current mirror circuit structured tocopy a current that flows through the diode, so as to generate thecorrection current.

Also, the multiple semiconductor light sources may be integrated on afirst semiconductor chip. Also, the multiple current sources may beintegrated on a second semiconductor chip. Also, the first semiconductorchip and the second semiconductor chip may be arranged such thatsurfaces thereof are coupled to each other so as to form a module housedin a single package.

With an embodiment, the lighting circuit may be provided to anautomotive lamp.

2. Another embodiment disclosed in the present specification relates toa driver circuit structured to supply a driving current to multiplesemiconductor light sources. The driver circuit includes: multiplecurrent sources each of which is to be coupled in series with acorresponding one from among the multiple semiconductor light sources;an interface circuit coupled to a processor, and structured to receive acontrol signal for indicating the on/off state of each of the multiplesemiconductor light sources, to generate multiple individual controlsignals based on the control signal so as to set the on/off state ofeach of the multiple current sources; and a protection circuitstructured to monitor communication between the processor and theinterface circuit, and to forcibly set each of the multiple currentsources to a predetermined state when an abnormal state has beendetected.

With the embodiment, when the control signal cannot be transmittednormally, the multiple current sources are each set to a predeterminedstate, thereby allowing a predetermined light distribution pattern to begenerated. This ensures a safety function that supports a situation inwhich an abnormal state has occurred in the lamp. More specifically,such an arrangement suppresses disturbance of leading vehicles oroncoming vehicles while securing a light distribution required fordriving the user's vehicle. That is to say, this arrangement providesboth high resolution and high safety.

Also, the predetermined state may correspond to a low-beam lightdistribution.

Also, the protection circuit may include: an abnormal state detectioncircuit structured to assert an abnormal state detection signal when anabnormal state has been detected; and a data replacement circuitstructured such that, when the abnormal state detection signal isnegated, the data replacement circuit outputs the multiple individualcontrol signals as they are, and such that, when the abnormal statedetection signal is asserted, the data replacement circuit outputs a setof predetermined values.

Also, the data replacement circuit may include: an inverter structuredto invert the abnormal state detection signal so as to generate aninverted abnormal state detection signal; multiple first logic gatesthat correspond to multiple current sources to be turned on when anabnormal state has been detected, from among the multiple currentsources; and multiple second logic gates that correspond to multiplecurrent sources to be turned off when an abnormal state has beendetected, from among the multiple current sources. Also, the first logicgates may each be structured to receive a corresponding individualcontrol signal and one from among the abnormal state detection signaland the inverted abnormal state detection signal, and to supply anoutput thereof to the corresponding current source. Also, the secondlogic gates may each be structured to receive a corresponding individualcontrol signal and the other one from among the abnormal state detectionsignal and the inverted abnormal state detection signal, and to supplyan output thereof to the corresponding current source.

Also, when there is no occurrence of level transition in the controlsignal for a predetermined period, the protection circuit may judge thatan abnormal state has occurred. This requires only a simple circuitconfiguration to detect the occurrence of an abnormal state incommunication.

Yet another embodiment disclosed in the present specification relates toan automotive lamp. The automotive lamp includes: a higher-levelcontroller; an interface circuit structured to receive a control signalfrom the higher-level controller; a variable light distribution device;a local controller structured to control the variable light distributiondevice based on the control signal received by the interface circuit;and an abnormal state detection unit structured to monitor communicationbetween the higher-level controller and the interface circuit so as todetect an abnormal state. The automotive lamp is configured such that,when an abnormal state has been detected, a predetermined pattern isforcibly set for the variable light distribution device.

With the embodiment, when the control signal cannot be transmittednormally, a desired light distribution pattern can be generatedaccording to a pattern set for the variable light distribution device.This suppresses disturbance of leading vehicles or oncoming vehicleswhile securing a light distribution required for driving the user'svehicle.

Also, the abnormal state detection unit may monitor an output of thelocal controller so as to detect an abnormal state. This arrangementprovides a safety function for handling a situation in which an abnormalstate has occurred in the local controller or a situation in which anabnormal state has occurred in communication between the localcontroller and the variable light distribution device.

EMBODIMENTS

Description will be made below regarding the present disclosure based onpreferred embodiments with reference to the drawings. The same orsimilar components, members, and processes are denoted by the samereference numerals, and redundant description thereof will be omitted asappropriate. The embodiments have been described for exemplary purposesonly, and are by no means intended to restrict the present disclosure.Also, it is not necessarily essential for the present disclosure thatall the features or a combination thereof be provided as described inthe embodiments.

In the present specification, the state represented by the phrase “themember A is coupled to the member B” includes a state in which themember A is indirectly coupled to the member B via another member thatdoes not substantially affect the electric connection between them, orthat does not damage the functions or effects of the connection betweenthem, in addition to a state in which they are physically and directlycoupled.

Similarly, the state represented by the phrase “the member C is providedbetween the member A and the member B” includes a state in which themember A is indirectly coupled to the member C, or the member B isindirectly coupled to the member C via another member that does notsubstantially affect the electric connection between them, or that doesnot damage the functions or effects of the connection between them, inaddition to a state in which they are directly coupled.

In the present specification, the reference symbols denoting electricsignals such as a voltage signal, current signal, or the like, and thereference symbols denoting circuit elements such as a resistor,capacitor, or the like, also represent the corresponding voltage value,current value, resistance value, or capacitance value as necessary.

Embodiment 1

FIG. 2 is a block diagram showing a lamp system 1 including anautomotive lamp 100 according to an embodiment 1. The lamp system 1includes a battery 2, an in-vehicle Electronic Control Unit (ECU) 4, andan automotive lamp 100. The automotive lamp 100 is configured as avariable light distribution headlamp having an ADB function. Theautomotive lamp 100 generates a light distribution according to acontrol signal received from the in-vehicle ECU 4.

The automotive lamp 100 includes multiple (N≥2) semiconductor lightsources 102_1 through 102_N, a lamp ECU 110, and a lighting circuit 200.Each semiconductor light source 102 may preferably be configured usingan LED. Also, various kinds of light-emitting elements such as an LD,organic EL, or the like, may be employed. Each semiconductor lightsource 102 may include multiple light-emitting elements coupled inseries and/or coupled in parallel. It should be noted that the number ofchannels, i.e., N, is not restricted in particular. Also, N may be 1.

The lamp ECU 110 includes a switch 112 and a microcontroller 114. Themicrocontroller (processor) 114 is coupled to the in-vehicle ECU 4 via abus such as a Controller Area Network (CAN) or Local InterconnectNetwork (LIN) or the like. This allows the microcontroller 114 toreceive various kinds of information such as a turn-on/turn-offinstruction, etc. The microcontroller 114 turns on the switch 112according to a turn-on instruction received from the in-vehicle ECU 4.In this state, a power supply voltage (battery voltage V_(BAT)) issupplied from the battery 2 to the lighting circuit 200.

Furthermore, the microcontroller 114 receives a control signal forindicating the light distribution pattern from the in-vehicle ECU 4, andcontrols the lighting circuit 200. Also, the microcontroller 114 mayreceive information that indicates the situation ahead of the vehiclefrom the in-vehicle ECU 4, and may autonomously generate the lightdistribution pattern based on the information thus received.

The lighting circuit 200 supplies the driving currents I_(LED1) throughI_(LEDN) to the multiple semiconductor light sources 102_1 through 102_Nso as to provide a desired light distribution pattern.

The lighting circuit 200 includes multiple current sources 210_1 through210_N, a switching converter 220, and a converter controller 230. Eachcurrent source 210_i (i=1, 2, . . . , N) is coupled to the correspondingsemiconductor light source 102_i in series. The current source 210_ifunctions as a constant current driver that stabilizes the drivingcurrent I_(LEDi) that flows through the semiconductor light source 102_ito a predetermined current amount.

The multiple current sources 210_1 through 210_N are each configured tobe capable of controlling their on/off states independently according toPWM signals S_(PWM1) through S_(PWMN) generated by the lightdistribution controller 116. When the PWM signal S_(PWMi) is set to theon level (e.g., high level), the driving current I_(LEDi) flows, therebyturning on the semiconductor light source 102_i. Conversely, when thePWM signal S_(PWMi) is set to the off level (e.g., low level), thedriving current I_(LEDi) is set to zero, thereby turning off thesemiconductor light source 102_i. By changing the duty ratio of the PWMsignal S_(PWMi), such an arrangement allows the effective luminance ofthe semiconductor light source 102_i to be changed (PWM dimming).

The switching converter 220 supplies a driving voltage V_(OUT) across aseries connection circuit of the semiconductor light source 102 and thecurrent source 210. The switching converter 220 is configured as astep-down converter (Buck converter) including a switching transistorM₁, a rectification diode D₁, an inductor L₁, and an output capacitorC₁.

In order to allow the current source 210 to maintain the driving currentI_(LED) at a predetermined amount, the voltage V_(CS) across the currentsource 210 is required to be higher than a predetermined threshold value(which will be referred to as a “saturation voltage V_(SAT)”). Theconverter controller 230 monitors the temperature T_(j), and controlsthe switching converter 220 based on a relation between the voltageV_(CS) across any one from among the multiple current sources 210 and areference voltage (which will be referred to as a “bottom limit voltageV_(BOTTOM)” hereafter) having a positive correlation with thetemperature T_(j). The bottom limit voltage V_(BOTTOM) is set such thatit is substantially the same as the saturation voltage V_(SAT) or suchthat it is slightly higher than the saturation voltage V_(SAT).

The converter controller 230 employs a ripple control method. Theconverter controller 230 turns on the switching transistor M₁ of theswitching converter 220 when the voltage V_(CS) across any one of themultiple current sources 210 decreases to the bottom limit voltageV_(BOTTOM). In the example shown in FIG. 2 , one end of each currentsource 210 is grounded. Accordingly, the voltage V_(LED) at a connectionnode that couples each current source 210 and the correspondingsemiconductor light source 102 is set to the voltage V_(CS) across thecurrent source 210.

Furthermore, when a predetermined turn-off condition is satisfied, theconverter controller 230 switches a control pulse S₁ to the off level(high level), thereby turning off the switching transistor M₁. Theturn-off condition may be that the output voltage V_(OUT) of theswitching converter 220 has reached a predetermined upper limit voltageV_(UPPER).

The above is the configuration of the automotive lamp 100. Next,description will be made regarding the operation thereof.

FIG. 3 is an operation waveform diagram showing the operation of theautomotive lamp 100 shown in FIG. 2 . For ease of understanding,description will be made regarding an example in which N=3. Furthermore,description will be made assuming that there is only negligible elementvariation between the multiple current sources 210_1 through 210_N.Furthermore, description will be made assuming that the relationV_(F1)>V_(F2)>V_(F3) holds true due to element variation between thesemiconductor light sources 102. For ease of understanding, descriptionwill be made regarding the operation without involving PWM dimming.

In the off period (low-level period in the drawing) of the switchingtransistor M₁, the output capacitor C₁ of the switching converter 220 isdischarged due to a load current I_(OUT) which is the sum total of thedriving currents I_(LED1) through I_(LED3), which lowers the outputvoltage V_(OUT) with time. In actuality, the output capacitor C₁ ischarged or discharged by the difference between the coil current I_(L)that flows through the inductor L₁ and the load current. Accordingly,the increase/decrease of the output voltage V_(OUT) does not necessarilymatch the on/off state of the switching transistor M₁ on the time axis.

The voltages that each occur across each current source 210, i.e., thevoltages (cathode voltages) V_(LED1) through V_(LED3) at the connectionnodes that each connect the corresponding current source 210 and thecorresponding semiconductor light source 102, are represented by thefollowing Expressions.V _(LED1) =V _(OUT) −V _(F1)V _(LED2) =V _(OUT) −V _(F2)V _(LED3) =V _(OUT) −V _(F3)

Accordingly, the voltages V_(LED1) through V_(LED3) each change whilemaintaining a constant voltage difference with respect to the outputvoltage V_(OUT). In this example, the forward voltage V_(F1) at thefirst channel is the largest value. Accordingly, the cathode voltageV_(LED1) at the first channel is the smallest value.

When the cathode voltage V_(LED1) at the first channel decreases to thebottom limit voltage V_(BOTTOM), the switching transistor M₁ is turnedon.

When the switching transistor M₁ is turned on, this raises the coilcurrent I_(L) that flows through the inductor L₁, which switches theoutput voltage V_(OUT) to an increasing phase. Subsequently, when theoutput voltage V_(OUT) reaches the upper limit voltage V_(UPPER), theswitching transistor M₁ is turned off. The lighting circuit 200 repeatsthis operation.

The above is the operation of the lighting circuit 200. The lightingcircuit 200 is capable of maintaining the voltage across each currentsource 210 at a level in the vicinity of the minimum level that ensuresthat each lighting circuit 200 is able to generate a predetermineddriving current I_(LED). This arrangement provides reduced powerconsumption.

As another approach (comparison technique), an arrangement isconceivable in which the cathode voltages V_(LED1) through V_(LEDN) arefeedback controlled using an error amplifier such that the minimumvoltage thereof approaches a predetermined target value V_(REF).

FIG. 4A is a waveform diagram showing the cathode voltage V_(LED)provided by the embodiment 1. FIG. 4B is a waveform diagram showing thecathode voltage V_(LED) provided by a comparison technique. The cathodevoltages V_(LED) shown in these drawings are each the lowest voltageV_(MIN) from among the multiple cathode voltages.

With the comparison technique, the average of the minimum voltageV_(MIN) from among the cathode voltages V_(LED1) through V_(LEDN)approaches the target voltage V_(REF) due to the responsecharacteristics of a phase compensation filter provided to a feedbackloop. That is to say, the bottom level V_(MIN_BOTTOM) of the minimumvoltage V_(MIN) is lower than the target voltage V_(REF). In this case,the difference between the bottom level V_(MIN_BOTTOM) and the targetvoltage V_(REF) changes in an unstable manner depending on thesituation. In order to provide stable circuit operation, as indicated bythe solid line in FIG. 4B, there is a need to set V_(REF) to a highvalue assuming that there is a large difference ΔV between the bottomlevel V_(MIN_BOTTOM) and the target voltage V_(REF). However, in asituation in which there is a small difference ΔV′ between them asindicated by the line of alternately long and short dashes, the cathodevoltage V_(LED) is higher than the bottom limit voltage V_(BOTTOM),leading to the occurrence of unnecessary power consumption in thecurrent source. With the embodiment 1, as shown in FIG. 4A, thisarrangement allows the bottom level of the cathode voltage V_(LED) toapproach the bottom limit voltage V_(BOTTOM), thereby providing furtherreduced power consumption as compared with the comparison technique.

Each current source 210 includes a transistor provided in series withthe corresponding semiconductor light source 102. By adjusting thevoltage and current applied to a control terminal (gate or base) of thetransistor, this arrangement allows the driving current I_(LED) to bemaintained at a constant level. FIG. 5 shows an example configuration ofthe multiple current sources 210_1 through 210_N. Each current source210_# (“#”=1, 2, . . . , N) is configured as a current mirror circuit216 including transistors M₃₁ and M₃₂. The input-side transistor M₃₁ iscoupled to a reference current source 218. A driving current I_(LED)flows through the output-side transistor M₃₂ with an amount of currentobtained by multiplying the reference current I_(REF) by a mirror ratio(K). A transistor M₃₃ is provided in order to control the on/off stateof the current source 210. The transistor M₃₃ is arranged between theground and a connection node that couples the gate and the drain of thetransistor M₃₁. When the S_(PWM)# signal is set to the high level, thetransistor M₃₃ is turned on, which turns off the current source 210. Inthis state, the current source 210 is turned off, and accordingly, thedriving current I_(LED) becomes zero. Conversely, when the S_(PWM)#signal is set to the low level, the transistor M₃₃ is turned off, whichturns on the current source 210. In this state, the current source 210is turned on, and accordingly, the driving current I_(LED) flows.

FIG. 6A is a diagram showing the I-V characteristics of a MOStransistor. FIG. 6B is a diagram showing a relation between thetemperature and the overdrive voltage. When the drain-source voltageV_(DS) is in a range that is higher than the overdrive voltage V_(OD)(or pinch-off voltage, or simply referred to as the “saturation voltageV_(DS(sat))”) the drain current I_(D) that flows through the MOStransistor becomes constant. The overdrive voltage V_(OD) is representedby the difference between the gate-source voltage V_(GS) and thethreshold voltage V_(GS(th)).V _(OD) =V _(GS) −V _(GS(th))

The threshold voltage V_(GS(th)) has a negative correlation with thetemperature. Accordingly, the overdrive voltage V_(OD) has a positivecorrelation with the temperature as shown in FIG. 6B. In a case in whicha bipolar transistor is employed instead of such a MOS transistor, theoverdrive voltage V_(OD) corresponds to a collector-emitter saturationvoltage V_(CE(sat)).

The current source 210 configured as the current mirror circuit shown inFIG. 5 is required to be designed to have an operation point in a rangewhere the voltage V_(CS) across the current source 210 is higher thanthe overdrive voltage V_(OD). In other words, the saturation voltageV_(SAT) of the current source 210 shown in FIG. 5 matches the overdrivevoltage V_(OD).

In the present embodiment 1, the bottom limit voltage V_(BOTTOM) ischanged such that it has a positive correlation with the temperatureT_(j). This arrangement allows the bottom limit voltage V_(BOTTOM) tofollow the change in the saturation voltage V_(SAT) (i.e., the overdrivevoltage V_(OD)) due to temperature variation.

As a comparison technique, description will be made regarding anarrangement in which the bottom limit voltage V_(BOTTOM) is set to aconstant value that is independent of the temperature. Description willbe made assuming that the semiconductor light source 102 has a maximumrated junction temperature T_(j) of 150° C., for example. In a case inwhich the semiconductor light source 102 and the current source 210 arearranged in the vicinity of each other or in a case in which they aremounted on a common heat sink, such an arrangement requires thesemiconductor light source 102 to have the same maximum rated junctiontemperature T_(j) of 150° C. In this case, in a case in which the bottomlimit voltage V_(BOTTOM) is set to the overdrive voltage V₁₅₀ at thetemperature T_(j) of 150° C., this allows a predetermined amount ofdriving current to be maintained even in a case of a high temperature ofup to 150° C. However, in actual operations, the junction temperature ofthe current source 210 is lower than 150° C. Accordingly, with thedifference between the overdrive voltage V_(OP) at the junctiontemperature in the actual operation and the overdrive voltage V₁₅₀ atthe temperature of 150° C. as ΔV_(LOSS), this leads to the occurrence ofexcess power loss of (I_(LED)×ΔV_(LOSS)). This leads to large heatgeneration. In a case in which there is no countermeasure for such aproblem, this lowers the allowable operating ambient temperature,resulting in degraded marketability of the automotive lamp 100. In acase in which an additional heat dissipation or cooling member such as alarge-size heat sink or a fan is provided in order to solve such aproblem, this leads to a problem of increased costs.

Conversely, in a case in which the bottom limit voltage V_(BOTTOM) isdesigned with the junction temperature T_(OP) in the normal operation asa reference, such an arrangement allows the power loss to be reducedwhen T_(j)=T_(OP). However, when the temperature becomes high (T_(j)becomes approximately 150° C.), such an arrangement cannot maintain apredetermined amount of driving current I_(LED), leading to a reductionin the luminance of the semiconductor light source 102.

As compared with the comparison technique, with the present embodiment1, the bottom limit voltage V_(BOTTOM) can be set to an optimum valuefor each temperature. This allows the power loss to be reduced in alow-temperature state. In addition, this arrangement is capable ofsuppressing a reduction of the luminance in a high-temperature state.

The present disclosure encompasses various kinds of apparatuses,circuits, and methods that can be regarded as a block configuration or acircuit configuration shown in FIG. 2 , or otherwise that can be derivedfrom the aforementioned description. That is to say, the presentdisclosure is not restricted to a specific configuration. More specificdescription will be made below regarding an example configuration or amodification for clarification and ease of understanding of the essenceof the present disclosure and the circuit operation. That is to say, thefollowing description will by no means be intended to restrict thetechnical scope of the present disclosure.

Example 1-1

FIG. 7 is a circuit diagram showing a converter controller 230Faccording to an example 1-1. An on signal generating circuit 240Fincludes multiple comparators 252_1 through 252_N, and a logic gate 254.Each comparator 252_i compares the corresponding cathode voltageV_(LEDi) with the bottom limit voltage V_(BOTTOM). The comparator 252_igenerates a comparison signal that is asserted (e.g., set to the highlevel) when V_(LEDi)<V_(BOTTOM). The logic gate 254 performs a logicaloperation on the outputs (comparison signals) S_(CMP1) through S_(CMPN)of the multiple comparators 252_1 through 252_N. When at least onecomparison signal is asserted, the logic gate 254 asserts the on signalS_(ON). In this example, the logic gate 254 is configured as an OR gate.

An off signal generating circuit 260F generates an off signal S_(OFF)which determines the timing at which the switching transistor M₁ is tobe turned off. A voltage dividing circuit 261 divides the output voltageV_(OUT) such that it is scaled to an appropriate voltage level. Acomparator 262 compares the output voltage V_(OUT)′ thus divided with athreshold value V_(UPPER)′ obtained by scaling the upper limit voltageV_(UPPER). When the relation V_(OUT)>V_(UPPER) is detected, thecomparator 262 asserts the off signal S_(OFF) (e.g., set to the highlevel).

The logic circuit 234 is configured as an SR flip-flop, for example. Thelogic circuit 234 switches its output Q to the on level (e.g., highlevel) in response to the assertion of the on signal S_(ON).Furthermore, the logic circuit 234 switches its output Q to the offlevel (e.g., low level) in response to the assertion of the off signalS_(OFF). It should be noted that the logic circuit 234 is preferablyconfigured as a reset-priority flip-flop in order to set the switchingconverter to a safer state (i.e., off state of the switching transistorM₁) when the assertion of the on signal S_(ON) and the assertion of theoff signal S_(OFF) occur at the same time.

A driver 232 drives the switching transistor M₁ according to the outputQ of the logic circuit 234. As shown in FIG. 2 , in a case in which theswitching transistor M₁ is configured as a P-channel MOSFET, when theoutput Q is set to the on level, the control pulse S₁, which isconfigured as the output of the driver 232, is set to a low voltage(V_(BAT)-V_(G)). When the output Q is set to the off level, the controlpulse S₁ is set to the high voltage (V_(BAT)).

FIG. 8 is a circuit diagram showing an example of a voltage generatingcircuit 280 that generates the bottom limit voltage V_(BOTTOM). Thevoltage generating circuit 280 includes a constant voltage source 282, acorrection current source 284, and a resistor R₅₁. The constant voltagesource 282 generates a constant voltage V_(CONST). The correctioncurrent source 284 generates a correction current I_(COMP) having apositive correlation with the junction temperature T_(j). The bottomlimit voltage V_(BOTTOM) is generated as a voltage obtained by addingthe constant voltage V_(CONST) to an offset voltage V_(OFS) that isproportional to the correction current I_(COMP). For example, one end ofa resistor R₅₁ may be coupled to an output of the constant voltagesource 282. Furthermore, a correction current I_(COMP) is applied to theone end of the resistor R₅₁ so as to generate a voltage drop(I_(COMP)×R₅₁) across the resistor R₅₁. The bottom limit voltageV_(BOTTOM) may be output as a voltage that occurs at the other end ofthe resistor R₅₁.V _(BOTTOM) =V _(CONST) +I _(COMP) ×R ₅₁

Description has been made in this example regarding an arrangement inwhich the source-type correction current source 284 is coupled to a highelectrical potential side of the resistor R₅₁. Also, the correctioncurrent source 284 configured as a sink-type current source may becoupled to a low electric potential side of the resistor R₅₁.

The configuration of the correction current source 284 is not restrictedin particular. For example, the correction current I_(COMP) may begenerated using the temperature dependence of the forward voltage Vf ofa PN junction. In FIG. 8 , the correction current source 284 includesmultiple diodes D₅₁ through D₅₃ and a resistor R₅₂ coupled in series,and a current mirror circuit 286 that copies a current It that flowsthrough the multiple diodes D₅₁ through D₅₃. With the forward voltage ofeach diode as Df, the current It is represented byIt=(V_(CC)−V_(BE)−3×Vf)/R₅₁.

In a case in which Vf is approximately equal to V_(BE), the current Itis represented by It=(V_(CC)−4×V_(BE))/R₅₁. Here, V_(BE) has a negativecorrelation with the temperature. Accordingly, the current It has apositive correlation with the temperature.

FIG. 9 is a circuit diagram showing another example of the voltagegenerating circuit 280 that generates the bottom limit voltageV_(BOTTOM). The voltage generating circuit 280 includes a current source288, a MOS transistor M₆₁, an emitter follower circuit 290, and aresistor network 292. The MOS transistor M₆₁ is provided on a path ofthe current I_(C) generated by the current source 288. The gate of theMOS transistor M₆₁ is biased such that the MOS transistor M₆₁ operatesin a linear region. For example, the power supply voltage V_(CC) isapplied to the gate via the resistor R₆₁. With such an arrangement, thedrain voltage V_(D) is proportional to the on resistance R_(ON).V _(D) =R _(ON) ×I _(C)

The on resistance R_(ON) of a MOS transistor has a positive correlationwith the temperature. Accordingly, the drain voltage V_(D) also has apositive correlation with the temperature. The drain voltage V_(D) isinput to an emitter follower circuit 290. The emitter follower circuit290 has a two-stage configuration including a PNP stage and an NPNstage. Such a configuration cancels out the base-emitter voltagesV_(BE). Accordingly, the output voltage of the emitter follower circuit290 is equal to the drain voltage V_(D) of the transistor M₆₁.

The resistor network 292 generates a weighted sum (average) of theconstant voltage V_(CONST) and the drain voltage V_(D) having a positivetemperature coefficient so as to generate the bottom limit voltageV_(BOTTOM). As a result, the bottom limit voltage V_(BOTTOM) has apositive temperature coefficient.

Example 1-2

FIG. 10 is a circuit diagram showing a comparator controller 230Gaccording to an example 1-2. An on signal generating circuit 240Gincludes a minimum value circuit 256 and a comparator 258. The minimumvalue circuit 256 outputs a voltage V_(MIN) that corresponds to theminimum value from among the multiple cathode voltages V_(LED1) throughV_(LEDN). The minimum value circuit 256 may preferably be configuredusing known techniques. The comparator 258 compares the voltage V_(MIN)with a threshold value V_(BOTTOM)′ that corresponds to the bottom limitvoltage V_(BOTTOM). When the relation V_(MIN)<V_(BOTTOM)′ holds true,the comparator 258 asserts the on signal S_(ON) (e.g., set to the highlevel). The bottom limit voltage V_(BOTTOM)′ has a positive correlationwith the temperature. In a case in which the relation between V_(MIN)and the minimum voltage from among V_(LED1) through V_(LEDN), i.e., Va,is represented by a function V_(MIN)=f (Va), the relation V_(BOTTOM)′=f(V_(BOTTOM)) holds true.

With the example 1-1, in a case in which there are a large number ofchannels, the circuit area required by the comparator group is large andthe chip size becomes large. In contrast, with the example 1-2, such anarrangement requires only a single comparator, thereby allowing thecircuit area to be reduced.

Example 1-3

FIG. 11 is a circuit diagram showing a converter controller 230Haccording to an example 1-3. With this example, the upper limit voltageV_(UPPER) is feedback controlled so as to maintain the switchingfrequency of the switching transistor M₁ at a constant value.

An off signal generating circuit 260H includes a frequency detectioncircuit 264 and an error amplifier 266 in addition to the comparator262. The frequency detection circuit 264 monitors the output Q of thelogic circuit 234 or the control pulse S₁, and generates a frequencydetection signal V_(FREQ) that indicates the switching frequency. Theerror amplifier 266 amplifies the difference between the frequencydetection signal V_(FREQ) and the reference voltage V_(FREQ(REF)) thatdefines a target value of the switching frequency, and generates theupper limit voltage V_(UPPER) that corresponds to the difference thusamplified.

With the example 1-3, this arrangement is capable of stabilizing theswitching frequency to a target value. This allows the noisecountermeasures to be provided in a simple manner.

Example 1-4

FIG. 12 is a circuit diagram showing a converter controller 230Iaccording to an example 1-4. The converter controller 230I may turn offthe switching transistor M₁ after the on time T_(ON) elapses after theswitching transistor M₁ is turned on. That is to say, as the turn-offcondition, a condition that the on time T_(ON) elapses after theswitching transistor M₁ is turned off may be employed.

An off signal generating circuit 260I includes a timer circuit 268. Thetimer circuit 268 starts the measurement of the predetermined on timeT_(ON) in response to the on signal S_(ON). After the on time T_(ON)elapses, the timer circuit 268 asserts (e.g., sets to the high level)the off signal S_(OFF). The timer circuit 268 may be configured as amonostable multivibrator (one-shot pulse generator), for example. Also,the timer circuit 268 may be configured as a digital counter or ananalog timer. In order to detect the timing at which the switchingtransistor M₁ is turned on, the timer circuit 268 may receive the outputQ of the logic circuit 234 or the control pulse S₁ as its input signalinstead of the on signal S_(ON).

Example 1-5

FIG. 13 is a circuit diagram showing a converter controller 230Jaccording to an example 1-5. As with the example 1-4, the convertercontroller 230J turns off the switching transistor M₁ after the on timeT_(ON) elapses after the switching transistor M₁ is turned on. An ORgate 241 corresponds to the on signal generating circuit, and generatesthe on signal S_(ON). The timer circuit 268 is configured as amonostable multivibrator or the like. The timer circuit 268 generatesthe pulse signal S_(P) that is set to the high level for a predeterminedon time T_(ON) after the assertion of the on signal S_(ON), and suppliesthe pulse signal S_(P) to the driver 232. It should be noted that,giving consideration to a situation in which the voltages V_(G1) throughV_(GN) are each lower than the threshold value of the OR gate 241 in thestartup operation or the like, an OR gate 231 is provided as anadditional component. With such an arrangement, the logical OR S_(P)′ ofthe on signal S_(ON) and the output S_(P) of the timer circuit 268 issupplied to the driver 232.

Example 1-6

FIG. 14 is a circuit diagram showing a converter controller 230Kaccording to an example 1-6. An off signal generating circuit 260Kfeedback controls the on time T_(ON) so as to maintain the switchingfrequency at a constant value. A variable timer circuit 270 isconfigured as a monostable multivibrator that generates the pulse signalS_(P) that is set to the high level during a period of the on timeT_(ON) after the assertion of the on signal S_(ON). The variable timercircuit 270 is configured to change the on time T_(ON) according to acontrol voltage V_(CTRL).

For example, the variable timer circuit 270 may include a capacitor, acurrent source that charges the capacitor, and a comparator thatcompares the voltage across the capacitor with a threshold value. Thevariable timer circuit 270 is configured such that at least one fromamong the current amount generated by the current source and thethreshold value can be changed according to the control voltageV_(CTRL).

The frequency detection circuit 272 monitors the output Q of the logiccircuit 234 or the control pulse S₁, and generates a frequency detectionsignal V_(FREQ) that indicates the switching frequency. An erroramplifier 274 amplifiers the difference between the frequency detectionsignal V_(FREQ) and the reference voltage V_(FREQ(REF)) that defines atarget value of the switching frequency, and generates the controlvoltage V_(CTRL) that corresponds to the difference thus amplified.

With the example 1-6, this arrangement is capable of stabilizing theswitching frequency to the target value, thereby allowing the noisecountermeasures to be provided in a simple manner.

FIG. 15 is a circuit diagram showing a specific configuration of theconverter controller 230K shown in FIG. 14 . Description will be maderegarding the operation of the frequency detection circuit 272. Acombination of a capacitor C₁₁ and a resistor R₁₁ functions as ahigh-pass filter, which can be regarded as a differentiating circuitthat differentiates the output of the OR gate 231 (or the control pulseS₁). Such a high-pass filter can also be regarded as an edge detectioncircuit that detects an edge of the pulse signal S_(P)′. When the outputof the high-pass filter exceeds a threshold value, i.e., when a positiveedge occurs in the pulse signal S_(P)′, a transistor Tr₁₁ turns on so asto discharge the capacitor C₁₂. During the off period of the transistorTr₁₁, the capacitor C₁₂ is charged via a resistor R₁₂. The voltageV_(C12) across the capacitor C₁₂ is configured as a ramp wave insynchronization with the pulse signal S_(P)′. The time length of theslope portion thereof, and the wave height that corresponds to the timelength of the slope portion, change according to the period of the pulsesignal S_(P)′.

A combination of the transistors Tr₁₂ and Tr₁₃, the resistors R₁₃ andR₁₄, and a capacitor C₁₃ is configured as a peak hold circuit. The peakhold circuit holds the peak value of the voltage V_(C12) across thecapacitor C₁₂. The output V_(FREQ) of the peak hold circuit has acorrelation with the period of the pulse signal S_(P)′, i.e., thefrequency thereof.

A comparator COMP1 compares the frequency detection signal V_(FREQ) withthe reference signal V_(FREQ(REF)) that indicates the target frequency.A combination of a resistor R₁₅ and a capacitor C₁₄ is configured as alow-pass filter. The low-pass filter smooths the output of thecomparator COMP1 so as to generate the control voltage V_(CTRL). Thecontrol signal V_(CTRL) is output via a buffer BUF1.

Description will be made regarding the variable timer circuit 270. Theon signal S_(ON) is inverted by an inverter 273. When the inverted onsignal #S_(ON) becomes lower than a threshold value V_(TH1), i.e., whenthe on signal S_(ON) is set to the high level, the output of acomparator COMP2 is set to the high level. This sets a flip-flop SREF,thereby setting the pulse signal S_(P) to the high level.

During the high-level period of the pulse signal S_(P), the transistorM₂₁ is turned off. During the off period of the transistor M₂₁, acurrent source 271 generates a variable current I_(VAR) that correspondsto the control voltage V_(CTRL) so as to charge a capacitor C₁₂. Whenthe voltage V_(C15) across the capacitor C₁₅ reaches a threshold valueV_(TH2), the output of the comparator COMP3 is set to the high level.This resets the flip-flop SREF, thereby switching the pulse signal S_(P)to the low level. As a result, the transistor M₂₁ is turned on, therebyinitializing the voltage V_(C15) of the capacitor C₁₅.

FIG. 16 is a circuit diagram showing a modification of the on signalgenerating circuit 240. In a case in which the comparator 252 isemployed as shown in FIG. 7 , this arrangement supports high-precisionvoltage comparison. However, such an arrangement has a tradeoff problemof a large circuit area and high costs. In order to solve such aproblem, as shown in FIG. 16 , a voltage comparison unit having a simpleconfiguration including a transistor may be employed. A voltagecomparison unit 253 includes an emitter follower circuit 255 including aPNP bipolar transistor Tr₂₁ and a comparison circuit 257. The output(V_(LED)+V_(BE)) of the emitter follower circuit 255 configured as anupstream stage is voltage divided by means of resistors R₂₁ and R₂₂, andthen input to the base of a transistor Tr₂₂. When the voltage V_(LED) tobe monitored decreases, the base voltage of the transistor Tr₂₂decreases. When the base voltage becomes lower than the on voltage ofthe bipolar transistor, the current that flows through the transistorTr₂₂ is cut off, which sets the output of the voltage comparison unit253 to the high level.

FIG. 16 shows an example in which the outputs of the multiple voltagecomparison units 253 are input to the OR gate 254. However, the presentdisclosure is not restricted to such an example. Also, such an OR gate254 may be omitted. With such an arrangement, the collectors of thetransistors Tr₂₂ of the multiple voltage comparison units 253 may becoupled so as to form a common collector. Also, a common resistor may beprovided between the common collector and the power supply line V_(CC).

FIGS. 17A through 17C are circuit diagrams each showing an exampleconfiguration of the current source 210. The current source 210 shown inFIG. 17A includes a series transistor M₂, a sensing resistor R_(S), andan error amplifier 212. The series transistor M₂ and the sensingresistor R_(S) are provided in series on a path of the driving currentI_(LEDi). The error amplifier 212 adjusts the voltage V_(G) at a controlelectrode (gate in this example) of the series transistor M₂ such thatthe voltage drop V_(CS) that occurs across the sensing resistor R_(S)approaches a target voltage V_(ADIM). In this example, the seriestransistor M₂ is configured as an N-type (N-channel) MOS transistor. Theerror amplifier 212 is arranged such that the reference voltage V_(ADIM)is input to one input thereof (non-inverting input terminal) and suchthat the voltage V_(CS) (voltage drop that occurs across the sensingresistor R_(S)) at a connection node that couples the series transistorM₂ and the sensing resistor R_(S) is input to the other input thereof(inverting input terminal). The error amplifier 212 provides feedbackcontrol such that V_(CS) approaches V_(ADIM), thereby stabilizing thedriving current I_(LED) with I_(LED(REF))=V_(ADIM)/R_(S) as its targetvalue.

The current source 210 further includes a switch (dimming switch) 214for PWM dimming. The dimming switch 214 is controlled according to a PWMsignal S_(PWM) generated by the dimming controller 116. When the dimmingswitch 214 is turned off, the driving current I_(LED) flows through thecurrent source 210. When the dimming switch 214 is turned on, the seriestransistor M₂ is turned off, which disconnects the driving currentI_(LED). The dimming switch 214 is switched at a high speed at a PWMfrequency of 60 Hz or more. Furthermore, by adjusting the duty ratio ofthe PWM frequency, the semiconductor light source 102 is subjected toPWM dimming control.

In the current source 210 shown in FIG. 17B, the series transistor isconfigured as a P-channel MOSFET. The error amplifier 212 is configuredto have an input polarity that is the reverse of that shown in FIG. 17A.

In a case of employing the current source 210 shown in FIG. 17A or 17B,the bottom limit voltage V_(BOTTOM) may preferably be determined asrepresented by the following Expression. Here, ΔV represents anappropriate margin.V _(BOTTOM) =R _(S) ×I _(LED) +V _(SAT) +ΔN

The current source 210 shown in FIG. 17C has the same configuration asthat shown in FIG. 5 , including a current mirror circuit 216 and areference current source 218. The current mirror circuit 216 multipliesthe reference current I_(REF) generated by the reference current source218 by a predetermined coefficient determined by a mirror ratio, so asto generate the driving current I_(LED). In a case of employing thecurrent source 210 shown in FIG. 17C, the bottom limit voltageV_(BOTTOM) may preferably be determined as represented by the followingExpression.V _(BOTTOM) =V _(SAT) +ΔV

Here, V_(SAT) represents the saturation voltage of the current mirrorcircuit, and ΔV represents an appropriate margin.

Embodiment 2

Next, description will be made regarding a light source with anintegrated driver. The multiple current sources 210 may be integrated ona single semiconductor chip, which will be referred as a “current driverIC (Integrated Circuit)” hereafter. FIG. 18 is a circuit diagram showinga current driver IC 300 and a peripheral circuit thereof according to anembodiment 2. In addition to multiple current sources 310_1 through310_N, the current driver IC 300 includes an interface circuit 320 and adimming pulse generator 330.

The multiple current sources 310_1 through 310_N are configured toswitch independently between the on state and the off state according toPWM signals S_(PWM1) through S_(PWMN), respectively. The current sources310_1 through 310_N are respectively coupled to the correspondingsemiconductor light sources 102_1 through 102_N in series via cathodepins LED1 through LEDN.

The interface circuit 320 receives multiple items of control data D₁through D_(N) from an external microcontroller (processor) 114. The kindof the interface is not restricted in particular. For example, a SerialPeripheral Interface (SPI) or I²C interface may be employed. Themultiple items of control data D₁ through D_(N) respectively indicatethe on/off duty ratios of the multiple current sources 310_1 through310_N, which are updated at a first time interval T₁. The first timeinterval T₁ is set to on the order of 20 ms to 200 ms. For example, thefirst time interval T₁ is set to 100 ms.

The dimming pulse generator 330 generates the multiple PWM signalsS_(PWM1) through S_(PWMN) for the multiple current sources 310_1 through310_N based on the multiple items of control data D₁ through D_(N). Inthe embodiment 1 (FIG. 2 ), the microcontroller 114 generates themultiple PWM signals S_(PWM1) through S_(PWMN). In the embodiment 2(FIG. 18 ), the current driver IC 300 has a built-in function ofgenerating the multiple PWM signals S_(PWM1) through S_(PWMN).

The duty ratio of the i-th PWM signal S_(PWMi) is gradually changed at asecond time interval T₂ that is shorter than the first time interval T₁from the corresponding control data D_(i) value before updating to theupdated value thereof (which will be referred to as the “gradual-changemode”). The second time interval T₂ is set to a value on the order of 1ms to 10 ms. For example, the second time interval T₂ is set to 5 ms.

The dimming pulse generator 330 is capable of supporting anon-gradual-change mode in addition to the gradual-change mode. In thenon-gradual-change mode, the duty ratio of the i-th PWM signal S_(PWMi)is allowed to be immediately changed from the corresponding control dataD_(i) value before updating to the updated value thereof.

The dimming pulse generator 330 may preferably be configured todynamically switch its mode between the non-gradual-change mode and thegradual-change mode according to the settings received from themicrocontroller 114. Preferably, the dimming pulse generator 330 isconfigured to dynamically switch its mode between the non-gradual-changemode and the gradual-change mode for each channel (for each dimmingpulse). The setting data that indicates the mode may be appended to thecontrol data D_(i).

A part of or the whole of the on signal generating circuit 240 may beintegrated on the current driver IC 300. The part of the on signalgenerating circuit 240 to be integrated may preferably be determinedaccording to the circuit configuration of the on signal generatingcircuit 240, and specifically, may preferably be determined so as toreduce the number of lines that couple the converter controller 230 andthe current driver IC 300. As shown in FIG. 18 , in a case in which theentire on signal generating circuit 240 is integrated on the currentdriver IC 300, such an arrangement requires only a single line betweenthe converter controller 230 and the current driver IC 300, which isused to transmit the on signal S_(ON). On the other hand, in a case ofemploying the on signal generating circuit 240G shown in FIG. 10 , andin a case in which the minimum value circuit 256 is integrated on thecurrent driver IC 300, such an arrangement requires only a single linebetween the converter controller 230 and the current driver IC 300,through which the minimum voltage V_(MIN) propagates.

Next, description will be made regarding the operation of the currentdriver IC 300. FIG. 19 is an operation waveform diagram showing theoperation of the current driver IC 300. Here, description will be madeassuming that the duty ratio of the PWM signal is changed linearly. Forexample, in a case in which T₁=100 ms, and T₂=5 ms, the duty ratio maypreferably be changed in a stepwise manner with 20 steps. With thedifference between the control data value before updating and thecontrol data value after updating as ΔX %, the duty ratio of the PWMsignal is changed in a stepwise manner with steps of ΔY=(ΔX/20)%.

The above is the operation of the current driver IC 300. The advantagesof the current driver IC 300 can be clearly understood in comparisonwith a comparison technique. If the current driver IC 300 does not havethe function of gradually changing the duty ratio, the microcontroller114 must update the control data D₁ through D_(N) that each indicate theduty ratio at the second time interval T₂. In a case in which the numberof channels N of the semiconductor light sources 102 exceeds severaldozen to 100, such an arrangement requires a high-performancemicrocontroller, i.e., a high-cost microcontroller, configured as themicrocontroller 114. Furthermore, such an arrangement requireshigh-speed communication between the microcontroller 114 and the currentdriver IC 300, thereby leading to the occurrence of a noise problem.

In contrast, with the current driver IC 300 according to the embodiment2, this arrangement allows the rate at which the microcontroller 114updates the control data D₁ through D_(N) to be reduced. This allows theperformance required for the microcontroller 114 to be reduced.Furthermore, this allows the communication speed between themicrocontroller 114 and the current driver IC 300 to be reduced, therebysolving the noise problem.

The first time interval T₁ may preferably be configured to be variable.In a situation in which there is only a small change in the duty ratio,the first time interval T₁ is increased so as to reduce the datacommunication amount, thereby allowing power consumption and noise to bereduced.

FIG. 19 shows an example in which the duty ratio is changed linearly.Also, the duty ratio may be changed according to a curve function suchas a quadratic function or an exponential function. In a case ofemploying such a quadratic function, this arrangement provides naturaldimming control with less discomfort.

As shown in FIG. 18 , the multiple semiconductor light sources 102_1through 102_N may be integrated on a single semiconductor chip (die)402. Furthermore, the semiconductor chip 402 and the current driver IC300 may be housed in a single package in the form of a module.

FIG. 20 shows a plan view and a cross-sectional view of theintegrated-driver light source 400. The multiple semiconductor lightsources 102 are formed in a matrix on the front face of thesemiconductor chip 402. The back face of the semiconductor chip 402 isprovided with pairs of back-face electrodes A and K that each correspondto a pair of an anode electrode and a cathode electrode of each of themultiple semiconductor light sources 102. In this drawing, only a singleconnection relation is shown for the semiconductor light source 102_1.

The semiconductor chip 402 and the current driver IC 300 aremechanically joined and electrically coupled. The front face of thecurrent driver IC 300 is provided with front-face electrodes 410 (LED1through LEDN in FIG. 18 ) to be respectively coupled to the cathodeelectrodes K of the multiple semiconductor light sources 102 andfront-face electrodes 412 to be respectively coupled to the anodeelectrodes A of the multiple semiconductor light sources 102. Eachfront-face electrode 412 is coupled to a corresponding bump (or pad) 414provided to a package substrate configured as a back face of the currentdriver IC 300. Also, an unshown interposer may be arranged between thesemiconductor chip 402 and the current driver IC 300.

The kind of the package of the integrated-driver light source 400 is notrestricted in particular. As the package of the integrated-driver lightsource 400, a Ball Grid Array (BAG), Pin Grid Array (PGA), Land GridArray (LGA), Quad Flat Package (QFP), or the like, may be employed.

In a case in which the semiconductor light sources 102 and the currentdriver IC 300 are each configured as a separate module, a countermeasuremay preferably be provided in which a heat dissipation structure or thelike is attached to each module. In contrast, with the integrated-driverlight source 400 as shown in FIG. 20 , there is a need to release thesum total of heat generated by the light sources 102 and the currentsources 210. Accordingly, such an arrangement has the potential torequire a very large heat dissipation structure. However, by employingthe lighting circuit 200 according to the embodiment 2, this arrangementis capable of suppressing heat generated by the current sources 210.This allows the size of the heat dissipation structure to be attached tothe integrated-driver light source 400 to be reduced.

Modification 1-1

Description will be made regarding a modification relating to theembodiments 1 and 2.

A desired transistor such as the series transistor M₂ may be configuredas a bipolar transistor. In this case, the base corresponds to the gate,the emitter corresponds to the source, and the collector corresponds tothe drain.

Modification 1-2

Description has been made in the embodiments regarding an arrangement inwhich the switching transistor M₁ is configured as a P-channel MOSFET.Also, an N-channel MOSFET may be employed. In this case, a bootstrapcircuit may be provided as an additional component. Instead of such aMOSFET, an Insulated Gate Bipolar Transistor (IGBT) or a bipolartransistor may be employed.

Modification 1-3

Description has been made in the embodiments regarding an arrangement inwhich the current source 210 is configured as a sink circuit, and iscoupled to the cathode of the corresponding semiconductor light source102. However, the present disclosure is not restricted to such anarrangement. FIG. 21 is a circuit diagram showing an automotive lamp 100according to a modification 1-3. In this modification, the cathodes ofthe semiconductor light sources 102 are coupled so as to form a commoncathode. Furthermore, each current source 210 configured as a sourcecircuit is coupled to the anode side of the corresponding semiconductorlight source 102. Each current source 210 may be configured bygeometrically reversing the configuration of the current source shown inFIG. 5 or 17 . The converter controller 230 controls the switchingconverter 220 based on the relation between the voltages V_(CS) thatoccur across each current source 210 and the bottom limit voltageV_(BOTTOM).

Embodiment 3

FIG. 24 is a block diagram showing a lamp system 1 including theautomotive lamp 100 according to an embodiment 3. The lamp system 1includes a battery 2, an in-vehicle Electronic Control Unit (ECU) 4, andan automotive lamp 100. The automotive lamp 100 is configured as avariable light distribution headlamp having an ADB function. Theautomotive lamp 100 generates a light distribution according to acontrol signal received from the in-vehicle ECU 4.

The automotive lamp 100 includes multiple (N≥2) semiconductor lightsources 102_1 through 102_N, a lamp ECU 110, a lighting circuit 200, anda current driver IC 300. Each semiconductor light source 102 maypreferably be configured using an LED. Also, various kinds oflight-emitting elements such as an LD, organic EL, or the like, may beemployed. Each semiconductor light source 102 may include multiplelight-emitting elements coupled in series and/or coupled in parallel. Itshould be noted that the number of the semiconductor light sources 102,i.e., N, is not restricted in particular. Specifically, the number N isat least several dozen or more, and is preferably several hundred toseveral thousand. Also, the number of channels, i.e., N, may be on theorder of tens of thousands. The multiple semiconductor light sources102_1 through 102_N are integrated on a single semiconductor chip (LEDchip 103).

The lamp ECU 110 includes a switch 112 and a microcontroller 114. Themicrocontroller (processor) 114 is coupled to the in-vehicle ECU 4 via abus such as a Controller Area Network (CAN) or Local InterconnectNetwork (LIN) or the like. This allows the microcontroller 114 toreceive various kinds of information such as a turn-on/turn-offinstruction, etc. The microcontroller 114 turns on the switch 112 inresponse to a turn-on instruction received from the in-vehicle ECU 4. Inthis state, a power supply voltage (battery voltage V_(BAT)) is suppliedfrom the battery 2 to the lighting circuit 200.

Furthermore, the microcontroller 114 receives a control signal forindicating the light distribution pattern from the in-vehicle ECU 4, andcontrols the lighting circuit 200. Also, the microcontroller 114 mayreceive information that indicates the situation ahead of the vehiclefrom the in-vehicle ECU 4, and may autonomously generate the lightdistribution pattern based on the information thus received.

The current driver IC 300 supplies the driving currents I_(LED1) throughI_(LEDN) to the multiple semiconductor light sources 102_1 through102_N. The current driver IC 300 is configured to capable ofindependently turning on and off the driving current I_(LED) for eachsemiconductor light source 102.

The lighting circuit 200 supplies the driving voltage V_(OUT) to the LEDchip 103 and the current driver IC 300. The lighting circuit 200 mayinclude the switching converter 220 and the converter controller 230. Inthis example, the switching converter 220 is configured as a step-downconverter. However, the topology of the switching converter 220 is notrestricted in particular.

The current driver IC 300 includes multiple current sources 310_1through 310_N, an interface circuit 320, a protection circuit 340, and afeedback circuit 360.

The current source 310_# (“#” represents 1 through N) is coupled inseries with the corresponding one 102_# from among the multiplesemiconductor light sources 102_1 through 102_N. The current source310_# is configured to be capable of switching its on/off stateaccording to a control input Sp_#. When the current source 310_# is setto the on state, the current source 310_# generates a driving currentI_(LED#). When the current source 310_# is set to the off state, thedriving current I_(LED#) is disconnected. For example, when the controlinput Sp_# is set to the high level, the current source 310_# is set tothe on state. Conversely, when the control input Sp_# is set to the lowlevel, the current source 310_# is set to the off state.

FIG. 25 is a circuit diagram showing an example configuration of themultiple current sources 310. Each current source 310 includes a currentmirror circuit 312, a reference current source 314, and a dimming switch316. The reference current source 314 generates a reference currentI_(REF). The current mirror circuit 312 copies the reference currentI_(REF), so as to generate a driving current I_(LED). The dimming switch316 is arranged between the gate and the source of the current mirrorcircuit 312. When the dimming switch 316 is turned on, the operation ofthe current mirror circuit 312 is suspended, thereby disconnecting thedriving current I_(LED). An inverter 318 inverts the control input Sp,and inputs the inverted control input to the gate of the dimming switch316. It should be noted that, in a case of employing a negative logicsystem, the inverter 318 may be omitted, and the semiconductor lightsource 102 may be turned on when the control input Sp is set to the lowlevel.

Returning to FIG. 24 , the feedback circuit 360 outputs a feedbacksignal S_(FB) to the converter controller 230 according to the voltagesV_(LED1) through V_(LEDN) that respectively occur across the multiplecurrent sources 310_1 through 310_N. For example, the feedback circuit360 is designed according to a control method of the convertercontroller 230.

The converter controller 230 may support a ripple control operation. Inthis case, when the lowest voltage from among the voltages V_(LED1)through V_(LEDN) that respectively occur across the current sources310_1 through 310_N decreases to a predetermined voltage (bottom limitvoltage V_(MIN)), the feedback circuit 360 may assert the feedbacksignal S_(FB). The converter controller 230 may turn on the switchingtransistor M₁ in response to the assertion of the feedback signalS_(FB).

The converter controller 230 may support a Pulse Width Modulation (PWM)control operation. The feedback circuit 360 may amplify the differencebetween a predetermined reference voltage V_(REF) and the lowest voltagefrom among the voltages V_(LED1) through V_(LEDN) that respectivelyoccur across the current sources 310_1 through 310_N, so as to generatethe feedback signal S_(FB) in the form of an analog signal. Also, theconverter controller 230 may generate a PWM signal having a duty ratiothat corresponds to the voltage level of the feedback signal S_(FB), soas to drive the switching transistor M₁.

In a case in which the feedback circuit 360 is built into the currentdriver IC 300, this allows the number of feedback paths to be reduced toone, thereby allowing the number of lines to be reduced.

The interface circuit 320 is coupled to the microcontroller (processor)114, and receives a control signal S1 that indicates the on/off state ofeach of the multiple semiconductor light sources 102_1 through 102_N.The interface circuit 320 has a decoder function of converting thecontrol signal S1 thus received into multiple individual control signalsS2_1 through S2_N. The multiple individual control signals S2_1 throughS2_N determine the on/off state of each of the multiple current sources310_1 through 310_N.

The protection circuit 340 monitors the communication between themicrocontroller 114 and the interface circuit 320. In a normal state,the individual control signals S2_1 through S2_N, which are generatedbased on the control signal S1, are supplied to the respective currentsources 310_1 through 310_N as they are. When the protection circuit 340has detected an abnormal state, the protection circuit 340 forcibly setsthe multiple current sources 310_1 through 310_N to a predeterminedstate. Specifically, the protection circuit 340 replaces the controlinputs Sp_1 through Sp_N, which are to be supplied to the currentsources 310_1 through 310_N, with a set of predetermined valuesindependent of the control signal S1 (individual control signals S2_1through S2_N).

For example, the predetermined state may correspond to a low-beam lightdistribution. FIG. 26 is a plan view of the LED chip 103. The LED chip103 is configured as an array of the multiple semiconductor lightsources 102 arranged in a matrix form. Each semiconductor light source102 corresponds to a pixel. A region RGN_(ON) to be turned on so as togenerate the low-beam light distribution is surrounded by the heavyline. When judgment has been made that an abnormal state has occurred,the multiple semiconductor light sources 102 included in the regionRGN_(ON) are forcibly turned on. The multiple semiconductor lightsources 102 included in a region to be turned off for the low-beam lightdistribution are forcibly turned off when judgement has been made thatan abnormal state has occurred.

FIG. 27 is a block diagram showing an example configuration of theinterface circuit 320 and the protection circuit 340. For example, theinterface circuit 320 may include a shift register 322 with an outputlatch. In this case, the interface circuit 320 and the lightdistribution controller 116 are coupled via three lines, i.e., an SDATAline, SCK line, and RCK line.

The shift register 322 with an output latch includes an N-bit shiftregister configured as an input stage and an N-bit storage registerconfigured as an output stage. The input-stage shift register acquiresserial data SDATA in synchronization with the SCK signal. Furthermore,the value acquired by the shift register is copied to the storageregister, and the value is updated, in response to a positive edge ofthe RCK signal. The values stored in the storage register are output asthe individual control signals S2_1 through S2_N.

The protection circuit 340 includes an abnormal state detection circuit342 and a data replacement circuit 344. The abnormal state detectioncircuit 342 monitors at least one from among the input signals of theinterface circuit 320 (SDATA, SCK, RCK, in this example), in order todetect the occurrence of an abnormal state in the communication. Forexample, when there is no change in a signal to be monitored for apredetermined period of time, the interface circuit 320 may judge thatan abnormal state has occurred. When judgement has been made that anabnormal state has occurred, an abnormal state detection signal S3 isasserted.

When the abnormal state detection signal S3 is negated, the datareplacement circuit 344 outputs the individual control signals S2_1through S2_N as they are. When the abnormal state detection signal S3 isasserted, the data replacement circuit 344 replaces the control inputsSp_1 through Sp_N for respectively controlling the multiple currentsources 310_1 through 310_N with predetermined values specified for therespective semiconductor light sources. Specifically, the input controlSp is set to “H” for each semiconductor light source 102 to be turned onin the abnormal state. On the other hand, for each semiconductor lightsource 102 to be turned off in the abnormal state, the input control Spis set to “L”.

FIGS. 28A and 28B are circuit diagrams each showing an exampleconfiguration of the data replacement circuit 344. The data replacementcircuit 344 shown in FIG. 28A includes an inverter 346, multiple firstlogic gates 348, and multiple second logic gates 350.

The inverter 346 inverts the abnormal state detection signal S3 so as togenerate an inverted abnormal state detection signal S3 b. The multiplefirst logic gates 348 respectively correspond to multiple currentsources to be turned on in the abnormal state from among the multiplecurrent sources 310. Each first logic gate 348_i receives thecorresponding individual control signal S2_i and one (S3 in thisexample) from among the abnormal state detection signal S3 and theinverted abnormal state detection signal S3 b, and supplies its outputto the corresponding current source 310_i. In this example, the firstlogic gate 348 is configured as an OR gate.

The multiple second logic gates 350 correspond to multiple currentsources to be turned off in the abnormal state from among the multiplecurrent sources 310. Each second logic gate 350_j receives thecorresponding individual control signal S2_j and the other one (S3 b inthis example) from among the abnormal state detection signal S3 and theinverted abnormal state detection signal S3 b, and supplies its outputto the corresponding current source 310_j. In this example, the secondlogic gate 350 is configured as an AND gate.

FIG. 28B shows another example configuration of the data replacementcircuit 344. The data replacement circuit 344 includes multipleselectors 352_1 through 352_N that correspond to the multiple currentsources 310_1 through 310_N. Each selector 352_# receives thecorresponding individual control signal S2_# and a predetermined valuea# as its input signals. The predetermined value a# is set to 1 for eachof the current sources 310_i to be turned on in the abnormal state. Onthe other hand, for each of the current sources 310_j to be turned offin the abnormal state, the predetermined value a# is set to 0. When theabnormal state detection signal S3 is negated (0), the selector 352_#selects the individual control signal S2_#. Conversely, when theabnormal state detection signal S3 is asserted (1), the selector 352_#selects the predetermined value a#. Such an arrangement shown in FIG.28B requires memory for storing the predetermined values al through a#.However, such an arrangement has an advantage of allowing the lightdistribution pattern to be generated in the abnormal state to be changedaccording to the value stored in the memory. In contrast, an arrangementshown in FIG. 28A has no function of changing the light distributionpattern to be generated in the abnormal state. However, such anarrangement does not require memory, thereby allowing the circuit areato be reduced.

FIG. 29 shows a plan view and a cross-sectional view of theintegrated-driver light source 400. The multiple semiconductor lightsources 102 are formed in a matrix on the front face of thesemiconductor chip 402 (LED chip in FIG. 24 ). The back face of thesemiconductor chip 402 is provided with pairs of back-face electrodes Aand K that each correspond to a pair of an anode electrode and a cathodeelectrode of each of the multiple semiconductor light sources 102. Inthis drawing, only a single connection relation is shown for thesemiconductor light source 102_1.

The semiconductor chip 402 and the current driver IC 300 aremechanically joined and electrically coupled. The front face of thecurrent driver IC 300 is provided with front-face electrodes 410 to berespectively coupled to the cathode electrodes K of the multiplesemiconductor light sources 102 and front-face electrodes 412 to berespectively coupled to the anode electrodes A of the multiplesemiconductor light sources 102. Each front-face electrode 412 iscoupled to a corresponding bump (or pad) 414 provided to a packagesubstrate configured as a back face of the current driver IC 300. Also,an unshown interposer may be arranged between the semiconductor chip 402and the current driver IC 300.

The kind of the package of the integrated-driver light source 400 is notrestricted in particular. As the package of the integrated-driver lightsource 400, a Ball Grid Array (BAG), Pin Grid Array (PGA), Land GridArray (LGA), Quad Flat Package (QFP), or the like, may be employed.

Lastly, description will be made regarding modifications thereof.

Modification 3.1

Description has been made in the embodiment 3 regarding an arrangementin which the current source 310 is configured as a sink circuit, and iscoupled to the cathode of the corresponding semiconductor light source102. However, the present disclosure is not restricted to such anarrangement. FIG. 30 is a circuit diagram showing an automotive lamp 100according to a modification 3.1. In this modification, the cathodes ofthe semiconductor light sources 102 are coupled so as to form a commoncathode. Furthermore, the current sources 310 configured as sourcecircuits are coupled to the anode sides of the correspondingsemiconductor light sources 102. In this example, the difference betweenV_(OUT) and V_(LED#) matches the voltage across the current source310_#. Accordingly, in a case in which the feedback circuit 360 employsa ripple control method, when the highest voltage from among the anodevoltages V_(LED1) through V_(LEDN) reaches a threshold voltage V_(TH)(=V_(OUT)−V_(MIN)), the feedback signal S_(FB) may be asserted. Here,V_(MIN) represents a minimum value of the voltage across the currentsource 310 which enables the operation of the current source 310. Also,the converter controller 230 may turn on the switching transistor M₁ inresponse to assertion of the feedback signal S_(FB).

Modification 3.2

Description has been made in the embodiment 3 regarding an arrangementin which the switching transistor M₁ is configured as a P-channelMOSFET. Also, the switching transistor M₁ may be configured as anN-channel MOSFET. In this case, a bootstrap circuit may be provided asan additional circuit. Instead of such a MOSFET, an Insulated GateBipolar Transistor (IGBT) or a bipolar transistor may be employed.

Modification 3.3

Description has been made in the embodiment 3 regarding an arrangementin which the logic circuit is configured as a positive logic system.However, the present disclosure is not restricted in particular. Also, apart of or the entire configuration of the logic circuit may beconfigured as a negative logic system.

Modification 3.4

The configuration of the current source 310 is not restricted to such anarrangement employing a current mirror circuit. Also, various kinds ofknown configurations may be employed.

Embodiment 4

FIG. 31 is a block diagram showing an automotive lamp 500 according toan embodiment 4. A lighting circuit 570 turns on a light source 560. Avariable light distribution device 530 includes multiple elements thatcan be controlled independently. The light distribution pattern isgenerated according to a state of the multiple controllable elements.For example, the variable light distribution device 530 is configured asa Digital Mirror Device (DMD) that reflects the output light of thelight source 560 or multiple bypass switches.

A lamp ECU 510 is configured as a higher-level controller that controlsthe light distribution pattern based on a control signal received fromthe in-vehicle ECU 4 via the communication line 5 and various kinds ofinformation.

A local controller 540 and the variable light distribution device 530are mounted on a single substrate 504. An interface circuit 520 iscoupled to the lamp ECU 510 via a communication line 502. The interfacecircuit 520 receives the control signal S1 that indicates the lightdistribution pattern. The local controller 540 controls the variablelight distribution device 530 based on the control signal S1 received bythe interface circuit 520. The local controller 540 may have a decoderfunction of converting the control signal S1 received from the lamp ECU510 into a control signal S4 for controlling the variable lightdistribution device 530. For example, the control signal S4 may includemultiple individual control signals that indicate the respective statesof the multiple controllable elements that form the variable lightdistribution device 530.

An abnormal state detection unit 550 monitors communication between thelamp ECU 510 and the interface circuit 520, and detects an abnormalstate based on the monitoring results. The automotive lamp 500 isconfigured such that, when an abnormal state has been detected by theabnormal state detection unit 550, a predetermined pattern is forciblyset for the variable light distribution device 530.

Upon detecting an abnormal state, the abnormal state detection unit 550asserts an abnormal state detection signal S5. For example, when thereis no change in the control signal S1 transmitted via the communicationline 502 for a predetermined period of time, the abnormal statedetection unit 550 may judge that an abnormal state has occurred. Inresponse to the assertion of the abnormal state detection signal S5, thelocal controller 540 sets the multiple individual control signals S2 toa set of predetermined values.

The interface circuit 520, the local controller 540, and the abnormalstate detection unit 550 may be configured as a single microcontroller.Also, the interface circuit 520, the local controller 540, and theabnormal state detection unit 550 may be configured as a combination ofmultiple hardware components.

The embodiment 3 can be regarded as a form of the embodiment 4, andthere is the following correspondence between them. Specifically, theinterface circuit 320 shown in FIG. 24 corresponds to the interfacecircuit 520 and the local controller 540 shown in FIG. 31 . Furthermore,the multiple current sources 310_1 through 310_N (or the multipledimming switches 316 included in the current sources 310_1 through310_M) shown in FIG. 24 correspond to the variable light distributiondevice 530 shown in FIG. 31 . Furthermore, the abnormal state detectioncircuit 342 shown in FIG. 27 corresponds to the abnormal state detectionunit 550 shown in FIG. 31 . The data replacement circuit 344 shown inFIG. 27 corresponds to a part of the local controller 540 shown in FIG.31 .

Modification 4.1

FIG. 32 is a block diagram showing an automotive lamp 500A according toa modification 4.1. The automotive lamp 500A further includes a selector552 and a fixed light distribution instruction unit 554 in addition tothe components of the automotive lamp 500 shown in FIG. 31 . The fixedlight distribution instruction unit 554 generates a control signal S6for determining a light distribution pattern to be used in an abnormalstate. When the abnormal state detection signal S5 is negated, theselector 552 selects the control signal S4 generated by the localcontroller 540. When the abnormal state detection signal S5 is asserted,the selector 552 selects the control signal S6 generated by the fixedlight distribution instruction unit 554.

Modification 4.2

FIG. 33 is a block diagram showing an automotive lamp 500B according toa modification 4.2. The automotive lamp 500B further includes a secondabnormal state detection unit 556 in addition to the components includedin the automotive lamp 500 shown in FIG. 32 . The second abnormal statedetection unit 556 monitors the output S4 of the local controller 540.Upon detecting an abnormal state, the second abnormal state detectionunit 556 asserts an abnormal state detection signal S7.

In response to the assertion of the abnormal state detection signal S5,the local controller 540 replaces the control signal S4 with a signal tobe used in the abnormal state.

In contrast, when the abnormal state detection signal S7 is asserted,this means that the local controller 540 is not operating normally, orthat an abnormal state has occurred in the communication line betweenthe local controller 540 and the variable light distribution device 530.In this state, such an arrangement is not able to supply the controlsignal S4 to be used in the abnormal state to the variable lightdistribution device 530. Accordingly, when the abnormal state detectionsignal S7 is asserted, the selector 552 selects the control signal S6generated by the fixed light distribution instruction unit 554. Thisallows a suitable control signal to be supplied to the variable lightdistribution device 530.

While the preferred embodiments of the present disclosure have beendescribed using specific terms, such description is for illustrativepurposes only, and it is to be understood that changes and variationsmay be made without departing from the spirit or scope of the appendedclaims.

What is claimed is:
 1. A lighting circuit structured to turn on and offa plurality of semiconductor light sources, the lighting circuitcomprising: a plurality of current sources each of which is to becoupled in series with a corresponding one of the plurality ofsemiconductor light sources; a switching converter structured to supplya driving voltage across each of a plurality of series connectioncircuits each of which include one of the plurality of semiconductorlight sources and one of the plurality of current sources; and aconverter controller structured to control the switching converter basedon a relation between a voltage across one of the plurality of currentsources and a reference voltage having a positive correlation withtemperature, wherein the converter controller monitors the temperatureand increases the reference voltage as the monitored temperatureincreases, wherein the converter controller turns on a switchingtransistor of the switching converter when the voltage across alowest-voltage one of the plurality of current sources decreases to thereference voltage, wherein the converter controller comprises: aconstant voltage source structured to generate a constant voltage; and acorrection current source structured to generate a correction currenthaving a positive correlation with temperature, wherein the referencevoltage matches a voltage obtained by adding the constant voltage to anoffset voltage that is proportional to the correction current.
 2. Thelighting circuit according to claim 1, wherein the current sourcecomprises a current mirror circuit.
 3. The lighting circuit according toclaim 1, wherein the correction current is generated using a temperaturedependence of a forward voltage provided by a PN junction.
 4. Thelighting circuit according to claim 1, wherein the correction currentsource comprises: at least one diode and a resistor coupled in series;and a current mirror circuit structured to copy a current that flowsthrough the diode, so as to generate the correction current.
 5. Thelighting circuit according to claim 1, wherein the plurality ofsemiconductor light sources are integrated on a first semiconductorchip, wherein the plurality of current sources are integrated on asecond semiconductor chip, and wherein the first semiconductor chip andthe second semiconductor chip are arranged such that surfaces thereofare coupled to each other so as to form a module housed in a singlepackage.
 6. An automotive lamp comprising the lighting circuit accordingto claim
 1. 7. A lighting circuit structured to turn on and off aplurality of semiconductor light sources, the lighting circuitcomprising: a plurality of current sources each of which is to becoupled in series with a corresponding one of the plurality ofsemiconductor light sources; a switching converter structured to supplya driving voltage across each of a plurality of series connectioncircuits each of which include one of the plurality of semiconductorlight sources and one of the plurality of current sources; and aconverter controller structured to control the switching converter basedon a relation between a voltage across one of the plurality of currentsources and a reference voltage having a positive correlation withtemperature, wherein the converter controller monitors the temperatureand increases the reference voltage as the monitored temperatureincreases, wherein the converter controller turns on a switchingtransistor of the switching converter when the voltage across alowest-voltage one of the plurality of current sources decreases to thereference voltage, wherein the converter controller comprises: a voltagesource; and a MOS transistor arranged on a path of an output current ofthe current source, and wherein the reference voltage corresponds to adrain-source voltage of the MOS transistor.
 8. The lighting circuitaccording to claim 7, wherein the current source comprises a currentmirror circuit.
 9. The lighting circuit according to claim 7, whereinthe converter controller comprises: a constant voltage source structuredto generate a constant voltage; and a correction current sourcestructured to generate a correction current having a positivecorrelation with temperature, wherein the reference voltage matches avoltage obtained by adding the constant voltage to an offset voltagethat is proportional to the correction current.
 10. The lighting circuitaccording to claim 9, wherein the correction current is generated usinga temperature dependence of a forward voltage provided by a PN junction.11. The lighting circuit according to claim 9, wherein the correctioncurrent source comprises: at least one diode and a resistor coupled inseries; and a current mirror circuit structured to copy a current thatflows through the diode, so as to generate the correction current. 12.The lighting circuit according to claim 7, wherein the plurality ofsemiconductor light sources are integrated on a first semiconductorchip, wherein the plurality of current sources are integrated on asecond semiconductor chip, and wherein the first semiconductor chip andthe second semiconductor chip are arranged such that surfaces thereofare coupled to each other so as to form a module housed in a singlepackage.
 13. An automotive lamp comprising the lighting circuitaccording to claim 7.